2-4
2 Operational Theory
2 Operational Theory
2 Operational Theory
2 Operational Theory
2 Operational Theory
TELEDYNE ANALYTICAL INSTRUMENTS
• Electropolished 316L-type stainless steel components.
To eliminate oxygen absorption and desorption from the internal
wetted surfaces of the sample system components, the sample system is
fabricated from electropolished 316L-type stainless steel.
• Welding/Metal Gasket-Type Fittings.
All of the joints upstream of the Micro-Fuel Cell oxygen sensor are
orbitally welded. Orbital welding is used in the sample system
wherever feasible. Orbital welding fuses the electropolished 316L
stainless steel components together, forming a smooth, clean internal
(wetted) weld junction and eliminating small spaces around the weld
junction where gases can get trapped or absorbed. All of the weld
junctions in the entire assembly are purged using an inert gas during
welding to ensure that there is no oxygen contamination.
Orbital welding is used where practical; otherwise, conventional
precision welding is used. For example, conventional precision welding
is used to fuse the tubes to the mounting blocks.
• Valves.
The analyzer sampling system utilizes three different types of valves.
Each valve is selected to prevent oxygen contamination of the sample
depending on its position and purpose in the circuit.
Air-Actuated Bellows Valves: These valves are normally closed in the
sample system. They are used to control the delivery through the sample
system of the sample or zero gas. The valve bodies are orbitally welded in
the system and the valve bonnets make a metal-to-metal seal to the body.
This valve system eliminates inboard and outboard gas leakage. The valves
are activated (open/closed) by computer-controlled solenoid valves.
Metering Valve: The metering valve is used to manually control the
gas flow rate to the sensor. The body of the metering valve is orbitally
welded, and the bonnet is sealed to the body with metal O-rings. This type of
valve eliminates inboard and outboard gas leakage.
Solenoid Valves: The solenoid valves control the air flow to the air-
activated bellows valves. The solenoid valves are controlled by the
microprocessor module. When de-energized, the valve outlet is open to
ambient air, allowing the air-activated bellows valve to close.
• Scrubber (optional). See Appendix for details.
In systems with a scrubber, oxygen-trapping media is used to remove
any trace oxygen from the sample gas. This occurs automatically in the
zero menu, where the pneumatic valves leading to the scrubber are
triggered by a certain menu sequence. This process enables sample gas
